This invention relates to a method for treating paint sludge, and more particularly, it relates to a method of treating paint sludge which may then be used as a polymeric component in various compounded polymeric compositions such as sealants, adhesives, plastics, rubbers and coatings.
The paint and coatings industry is a major source of chemical wastes. Paint wastes or sludges are produced in the appliance industry, metal fabricating industry, and the automobile industry. For example, it is estimated that nearly 40% of the 6 gallons of paint used to produce the exterior finish on an automobile ends up as waste. Paint sludges are also produced during the painting of wood products, outdoor structures such as bridges and lamp posts, and all types of industrial equipment. Unused or left-over paint requiring disposal is also a "paint sludge" to be dealt with.
Paint sludge typically contains uncured polymer resins, pigments, curing agents, surfactants, and other minor formulation ingredients. In addition, paint sludge typically contains water and/or a variety of organic solvents.
The cost and the environmental impact of disposing of paint sludge has been a source of concern in the industry.
However, in recent years, several processes have been developed for converting paint sludge into useful products, thereby reducing a major source of chemical waste.
One such process is disclosed in U.S. Pat. No. 4,980,030, which includes removing a portion of the water and liquid hydrocarbons from the sludge. The high solids sludge is then heated to remove the remaining water and hydrocarbons. The heating step is also designed to cure the uncured polymeric paint resins. The process is advantageous because it reduces the volume of waste produced, and produces a powder which is somewhat easier to handle than the wet sludge.
A similar process is disclosed in U.S. Pat. No. 5,087,375, which discloses a method of heating and calcining paint sludge to form a product which may be used as a filler for sealants.
However, both U.S. Pat. Nos. 4,980,030 and 5,087,375, completely cure any uncured polymers in the paint sludge during their heating and/or calcining steps. Accordingly, the resulting product is an inert, inorganic, brittle, abrasive particulate material.
An improved process is disclosed in U.S. Pat. Nos. 5,160,628, and 5,254,263, assigned to the same assignee as the present invention, which disclose a product formed from paint sludge containing water, solvent and uncured polymer resin which may be used as a filler in sealant compositions. By keeping the polymer uncured, the resulting product is soft and easily dispersible. However, this process requires that the heating temperature must not exceed 100.degree. F. so that the polymer remains uncured.
Further, fillers are only one of several components of sealants and other related compositions, which are generally comprised of other components such as polymers and plasticizers. Such components typically comprise up to 75% or more of the total compounded polymeric composition, and polymers in particular usually account for a significant portion of the cost of sealant formulations. It would be desirable to be able use paint sludge as a replacement for one of the polymeric components in sealants and other related compositions to reduce production costs.
Accordingly, the need remains for a method of treating paint sludge containing uncured polymer resins, water and/or solvent to form sealant compositions and related products which utilize paint sludge as a polymeric component thereof, which are cost effective to produce, and which do not require complex processing steps.